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Abstract:

A hybrid construction machine is capable of performing satisfactory
operations even when trouble occurs that disables the electric motor from
outputting torque. The hybrid construction has both a hydraulic motor and
an electric motor driving the swing structure and a controller for
switching between a hydraulic/electric hybrid swing mode (using both the
hydraulic motor and the electric motor) and a hydraulic-alone swing mode
(using only the hydraulic motor). The switching is executed while
achieving satisfactory operability and performance in each mode.
Normally, an energy saving operation is performed in the
hydraulic/electric hybrid swing mode. When the electric amount of an
electricity storage device has gone out of a prescribed range or an
abnormality has occurred in an electric system (e.g., failure of an
inverter), the swing mode is switched to the hydraulic-alone swing mode
so that driving with normal braking torque is possible by the hydraulic
motor alone.

Claims:

1. A hybrid construction machine comprising: a prime mover; a hydraulic
pump driven by the prime mover; a swing structure; an electric motor for
driving the swing structure; a hydraulic motor for driving the swing
structure, and the hydraulic motor being driven by the hydraulic pump; an
electricity storage device connected to the electric motor; a swing
control lever device which outputs a command regarding the driving of the
swing structure; a control device which switches a swing mode regarding
the driving of the swing structure between: a hydraulic/electric hybrid
swing mode for driving the swing structure by total torque of the
electric motor and the hydraulic motor by driving both the electric motor
and the hydraulic motor when the swing control lever device is operated,
and a hydraulic-alone swing mode for driving the swing structure by the
torque of the hydraulic motor alone by driving only the hydraulic motor
when the swing control lever device is operated.

2. The hybrid construction machine according to claim 1, wherein: the
control device drives the swing structure in the hydraulic/electric
hybrid swing mode in a normal operation state, and the control device
automatically switches the swing mode from the hydraulic/electric hybrid
swing mode to the hydraulic-alone swing mode when a predetermined type of
failure, abnormality or warning state has occurred in an electric system
for the driving of the electric motor including the electric motor and
the electricity storage device.

3. The hybrid construction machine according to claim 2, wherein the
control device automatically switches the swing mode from the
hydraulic-alone swing mode to the hydraulic/electric hybrid swing mode
when the failure, abnormality or warning has been eliminated.

4. The hybrid construction machine according to claim 1, wherein: the
control device drives the swing structure in the hydraulic/electric
hybrid swing mode when the amount of electricity stored in the
electricity storage device is within a prescribed range, and the control
device automatically switches the swing mode from the hydraulic/electric
hybrid swing mode to the hydraulic-alone swing mode when the amount of
electricity stored in the electricity storage device has gone out of the
prescribed range.

5. The hybrid construction machine according to claim 1, wherein the
control device executes the switching between the hydraulic/electric
hybrid swing mode and the hydraulic-alone swing mode exclusively in a
state in which the swing structure is not moving.

6. The hybrid construction machine according to claim 1, wherein the
control device executes the switching between the hydraulic/electric
hybrid swing mode and the hydraulic-alone swing mode exclusively in a
state in which the swing structure is not moving and the swing control
lever device is not being operated.

7. The hybrid construction machine according to claim 1, wherein the
control device executes the switching between the hydraulic/electric
hybrid swing mode and the hydraulic-alone swing mode exclusively in a
state in which there is no movement of the swing structure, no input to
the swing control lever device, no movement of the devices other than the
swing structure and no input to an operating device for the prescribed
devices other than the swing structure.

8. The hybrid construction machine according to claim 1, wherein: the
hydraulic motor is capable of outputting maximum torque sufficient for
independently driving the swing structure, and maximum torque of the
electric motor is lower than the maximum torque of the hydraulic motor.

9. The hybrid construction machine according to claim 1, wherein: the
control device charges the electricity storage device with a charging
device when the amount of electricity stored in the electricity storage
device just after startup of the construction machine is lower than a
prescribed electric amount necessary for the operation in the
hydraulic/electric hybrid swing mode, the control device executes the
swing operation in the hydraulic-alone swing mode when the swing control
lever device is operated during the charging process, and the control
device switches the swing mode to the hydraulic/electric hybrid swing
mode after the amount of electricity stored in the electricity storage
device has reached the prescribed electric amount.

10. The hybrid construction machine according to claim 1, wherein: the
control device discharges the electricity storage device when the amount
of electricity stored in the electricity storage device just after
startup of the construction machine is higher than a prescribed electric
amount necessary for the operation in the hydraulic/electric hybrid swing
mode, the control device executes the swing operation in the
hydraulic-alone swing mode when the swing control lever device is
operated during the discharging process, and the control device switches
the swing mode to the hydraulic/electric hybrid swing mode after the
amount of electricity stored in the electricity storage device has
reached the prescribed electric amount.

11. The hybrid construction machine according to claim 1, wherein: the
prime mover is an electric motor, and the electric motor is powered by a
AC power supply.

12. The hybrid construction machine according to claim 1, wherein: the
prime mover is an electric motor, and the electric motor is powered by
the electricity storage device.

13. The hybrid construction machine according to claim 1, further
comprising: an electric power control unit which controls transfer of
electric power between the electricity storage device and the electric
motor; and a swing hydraulic system which includes a swing spool for
controlling the flow of hydraulic fluid supplied from the hydraulic pump
to the hydraulic motor and the flow of the hydraulic fluid returned from
the hydraulic motor to a tank, wherein: the swing hydraulic system is
switchable between a first mode in which maximum output torque of the
hydraulic motor equals first torque and a second mode in which the
maximum output torque of the hydraulic motor equals second torque that is
higher than the first torque, and the control device includes: a
hydraulic/electric hybrid swing control unit which switches the swing
hydraulic system to the first mode and which outputs a torque command to
the electric power control unit and thereby drives the electric motor
when the swing control lever device is operated; and a hydraulic-alone
swing control unit which switches the swing hydraulic system to the
second mode and stops the output of the torque command to the electric
power control unit, and the control device executes the switching between
the hydraulic/electric hybrid swing mode and the hydraulic-alone swing
mode by selecting one from the hydraulic/electric hybrid swing control
unit and the hydraulic-alone swing control unit.

14. The hybrid construction machine according to claim 13, wherein the
control device further includes an abnormality monitoring/control unit
which selects the hydraulic/electric hybrid swing control unit in a
normal operation state and selects the hydraulic-alone swing control unit
when a prescribed type of failure, abnormality or warning state has
occurred in an electric system including the electric motor, the
electricity storage device and the electric power control unit.

15. The hybrid construction machine according to claim 13, wherein the
control device further includes an energy management control unit which
selects the hydraulic/electric hybrid swing control unit when the amount
of electricity stored in the electricity storage device is within a
prescribed range and selects the hydraulic-alone swing control unit when
the amount of electricity stored in the electricity storage device has
gone out of the prescribed range.

Description:

TECHNICAL FIELD

[0001] The present invention relates to a hybrid construction machine. The
invention more particularly relates to a hybrid construction machine
having a swing structure such as a hydraulic shovel.

BACKGROUND ART

[0002] A construction machine such as a hydraulic shovel uses fuel
(gasoline, light oil, etc.) as the power source of its engine and drives
hydraulic actuators (hydraulic motor, hydraulic cylinder, etc.) using
hydraulic pressure generated by a hydraulic pump which is driven by the
engine. Being small-sized, lightweight and capable of outputting high
power, the hydraulic actuators are widely used as actuators for
construction machines.

[0004] Electric motors (electric actuators) have some excellent features
in terms of energy, such as higher energy efficiency compared to
hydraulic actuators and the ability to regenerate electric energy from
kinetic energy at the time of braking. The kinetic energy is released and
lost as heat in the case of hydraulic actuators.

[0005] For example, Patent Document 1 discloses an embodiment of a
hydraulic shovel having an electric motor as the actuator for driving the
swing structure. The actuator for driving and swinging the upper swing
structure of the hydraulic shovel with respect to the lower travel
structure (a hydraulic motor was used in conventional hydraulic shovels)
is used frequently and repeats start/stop and acceleration/deceleration
frequently in work.

[0006] When a hydraulic actuator is used for driving the swing structure,
the kinetic energy of the swing structure in deceleration (braking) is
lost as heat in the hydraulic circuit. In contrast, energy saving can be
realized by use of an electric motor since regeneration of the kinetic
energy into electric energy is expected.

[0007] There have also been proposed and disclosed construction machines
that are equipped with both a hydraulic motor and an electric motor so as
to drive the swing structure by total torque of the hydraulic motor and
the electric motor (Patent Documents 2 and 3).

[0008] Patent Document 2 discloses an energy regeneration device of a
hydraulic construction machine in which an electric motor is connected
directly to the hydraulic motor for driving the swing structure. A
controller determines the output torque of the electric motor based on
the operation amount of the control lever and sends an output torque
command to the electric motor. In deceleration (braking), the electric
motor regenerates the kinetic energy of the swing structure into electric
energy and accumulates the regenerated energy in a battery.

[0009] Patent Document 3 discloses a hybrid construction machine which
performs output torque splitting between the hydraulic motor and the
electric motor by calculating a torque command value for the electric
motor using the differential pressure between the inlet side and the
outlet side of the hydraulic motor for the swing driving.

[0010] Both of the conventional techniques of Patent Documents 2 and 3 use
an electric motor and a hydraulic motor together as the actuators for the
swing driving and thereby realize operation with no feeling of
strangeness even for operators familiar with conventional construction
machines driven by a hydraulic actuator, as well as achieving energy
saving with a configuration that is simple and easy to put into practical
use.

PRIOR ART DOCUMENT

Patent Document

[0011] Patent Document 1: Japanese Patent No. 3647319

[0012] Patent Document 2: Japanese Patent No. 4024120

[0013] Patent Document 3: JP,A 2008-63888

SUMMARY OF THE INVENTION

Problem to be Solved by the Invention

[0014] In the hybrid hydraulic shovel described in the Patent Document 1,
the kinetic energy of the swing structure in deceleration (braking) is
regenerated by the electric motor into electric energy, which is
effective from the viewpoint of energy saving.

[0015] However, using an electric motor, having different characteristics
from hydraulic motors, for driving the swing structure of a construction
machine can cause the following problems:

[0016] (1) Hunting (especially in a low speed range, stopped state) due to
inappropriate speed feedback control of the electric motor, etc.

[0017] (2) Feeling of strangeness about the operation (manipulation) of
the construction machine caused by the difference in characteristics from
hydraulic motors.

[0018] (3) Overheating of the motor or inverter during an operation/work
(e.g., pressing operation) that requires continuous torque output with no
rotation of the motor.

[0019] (4) Increase in the size of the motor or considerable increase in
costs due to the use of an electric motor guaranteeing high output
equivalent to that of hydraulic motors.

[0020] The hybrid hydraulic shovels described in the Patent Documents 2
and 3 solve the above problems by employing both a hydraulic motor and an
electric motor and driving the swing structure by the total torque of the
motors, thereby realizing operation with no feeling of strangeness even
for operators familiar with conventional construction machines driven by
a hydraulic actuator, as well as achieving energy saving with a
configuration that is simple and easy to put into practical use.

[0021] However, in every one of the conventional techniques described in
the above Patent Documents 1 to 3, the electric motor is constantly
accounted for a certain part of the total torque necessary for the swing
driving. Therefore, when the electric motor is incapable of generating
torque for some reason (failure/abnormality in an electric system
(inverter, motor, etc.), a low energy state or an overcharged state of
the electricity storage device, etc.), the total torque becomes
insufficient for driving the swing structure and it becomes impossible to
start/stop the swing structure as in the normal state.

[0022] For example, if an abnormality occurs suddenly when the swing
structure is swinging at a high speed with high kinetic energy, the
electric motor falls into a free running state and cannot be stopped by
the conventional technique of Patent Document 1. Even with the
conventional techniques of Patent Documents 2 and 3, the stopping
distance and the stopping time increase compared to the normal state,
which can lead to a serious problem in terms of safety.

[0023] Further, the amount of energy stored in the electricity storage
device can be too small just after the startup of the machine due to
self-discharge of the electricity storage device while the machine is
stopped/stored, etc. In this case, the swing operation cannot be started
immediately because of the electric swing motor being incapable of
outputting power. Since it is first necessary to charge the electricity
storage device until a prescribed amount of electricity is accumulated,
the operator has to wait on standby for the completion of the charging
even when work should be started immediately.

[0024] It is therefore the primary object of the present invention to
provide a hybrid construction machine (construction machine using an
electric motor for the driving of the swing structure) capable of
performing satisfactory operations even when trouble disabling the
electric motor from outputting torque has occurred for some reason.

Means for Solving the Problem

[0025] A hybrid construction machine in accordance with the present
invention includes both a hydraulic motor and an electric motor for the
driving of the swing structure and a swing mode regarding the driving of
the swing structure is switched by a control device between a
hydraulic/electric hybrid swing mode for driving the swing structure by
driving both the hydraulic motor and the electric motor and a
hydraulic-alone swing mode for driving the swing structure by driving
only the hydraulic motor. The switching between the hydraulic/electric
hybrid swing mode and the hydraulic-alone swing mode is executed while
achieving satisfactory operability and performance in each mode.
Normally, an energy saving operation is performed in the
hydraulic/electric hybrid swing mode. When the amount of electricity of
the electricity storage device has gone out of a prescribed range or an
abnormality has occurred in an electric system (e.g., failure of an
inverter), the swing mode is switched to the hydraulic-alone swing mode
so that driving with normal braking torque is possible by the hydraulic
motor alone even when the electric motor falls into a free running state.

Effect of the Invention

[0026] According to the present invention, the construction machine is
equipped with both a hydraulic motor and an electric motor for the
driving of the swing structure and is configured to be switchable between
the mode for executing the swing driving with the torque of both the
hydraulic motor and the electric motor (hydraulic/electric hybrid swing
mode) and the mode for executing the swing driving with the hydraulic
motor alone (hydraulic-alone swing mode). Thus, in the hydraulic/electric
hybrid swing mode, operational actions specific to the hydraulic actuator
(e.g., pressing excavation) and operational feeling specific to the
hydraulic actuator can be realized while also achieving energy saving by
regenerating the kinetic energy of the swing structure into electric
energy through the electric motor at the time of braking (deceleration).
Even in case of insufficiency of the energy remaining in the electricity
storage device for storing the regenerated electric energy, overcharging
of the electricity storage device, or a failure, abnormality or warning
occurring in the electric system, it is possible to drive the swing
structure with normal swing torque using the hydraulic motor alone and
continue the operation (work) by the switching of the swing mode to the
hydraulic-alone swing mode. Furthermore, even when the energy remaining
in the electricity storage device is insufficient at the startup of the
construction machine, the operation (work) can be started immediately.

[0027] As above, the present invention enables construction machines to
perform satisfactory operations even when trouble disabling the electric
motor from outputting torque has occurred for some reason.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a side view of a hybrid hydraulic shovel in accordance
with a first embodiment of the present invention.

[0029]FIG. 2 is a system configuration diagram showing principal
electric/hydraulic devices of the hybrid hydraulic shovel in accordance
with the first embodiment of the present invention.

[0030]FIG. 3 is a block diagram showing the system configuration and
control blocks of the hybrid hydraulic shovel in accordance with the
first embodiment of the present invention.

[0031]FIG. 4 is a schematic diagram showing the configuration of a swing
hydraulic system in the first embodiment of the present invention.

[0032]FIG. 5 is a graph showing the torque control characteristics of a
hydraulic pump in the first embodiment of the present invention.

[0033]FIG. 6A is a graph showing a meter-in opening area characteristic
and a bleed-off opening area characteristic of a swing spool in the first
embodiment of the present invention.

[0034]FIG. 6B is a graph showing a meter-out opening area characteristic
of the swing spool in the first embodiment of the present invention.

[0035]FIG. 7 is a graph showing a combined opening area characteristic of
a meter-in restrictor of a swing spool and a center bypass cut valve with
respect to a hydraulic pilot signal (operating pilot pressure) in the
first embodiment of the present invention.

[0036] FIG. 8 is a graph showing time-series waveforms of the hydraulic
pilot signal (pilot pressure), meter-in pressure (M/I pressure), assist
torque of a electric swing motor and revolution speed (swing speed) of an
upper swing structure in a swing driving operation in a
hydraulic/electric hybrid swing mode in the first embodiment of the
present invention.

[0037]FIG. 9 is a graph showing a meter-out opening area characteristic
of the swing spool with respect to the hydraulic pilot signal (operating
pilot pressure) in the first embodiment of the present invention.

[0038]FIG. 10 is a graph showing time-series waveforms of the hydraulic
pilot signal (pilot pressure), meter-out pressure (M/O pressure), the
assist torque of the electric swing motor and the revolution speed (swing
speed) of the upper swing structure in a swing braking/stopping operation
in the hydraulic/electric hybrid swing mode in the first embodiment of
the present invention.

[0039] FIG. 11 is a graph showing relief pressure characteristics of
variable over-load relief valves for the swing in the first embodiment of
the present invention.

[0040]FIG. 12 is a flow chart showing an abnormality processing sequence
(switching from the hydraulic/electric hybrid swing mode to a
hydraulic-alone swing mode) of the hybrid hydraulic shovel in accordance
with the first embodiment of the present invention.

[0041]FIG. 13 is a flow chart showing an abnormality processing sequence
(returning to the hydraulic/electric hybrid swing mode) of the hybrid
hydraulic shovel in accordance with the first embodiment of the present
invention.

[0042]FIG. 14 is a flow chart showing a startup sequence of an ordinary
hydraulic shovel.

[0043]FIG. 15 is a flow chart showing a startup sequence of a
conventional hybrid hydraulic shovel having a capacitor and a electric
swing motor.

[0044]FIG. 16 is a flow chart showing a startup sequence of the hybrid
hydraulic shovel in accordance with the first embodiment of the present
invention.

[0045]FIG. 17 is a system configuration diagram showing principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a second embodiment of the present invention.

[0046]FIG. 18 is a system configuration diagram showing principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a third embodiment of the present invention.

[0047]FIG. 19 is a system configuration diagram showing principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a fourth embodiment of the present invention.

[0048]FIG. 20 is a system configuration diagram showing principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a fifth embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

[0049] In the following, preferred embodiments in accordance with the
present invention will be described by taking hydraulic shovels as
examples of construction machines. The present invention is applicable to
a wide variety of construction machines (e.g., operating machines) having
a swing structure and thus the application of the present invention is
not restricted to hydraulic shovels. For example, the present invention
is applicable also to other types of construction machines such as crane
trucks having a swing structure.

[0050]FIG. 1 is a side view of a hybrid hydraulic shovel in accordance
with a first embodiment of the present invention.

[0052] The lower travel structure 10 includes a pair of crawlers 11a and
11b, a pair of crawler frames 12a and 12b (only one side is shown in FIG.
1), a pair of traveling hydraulic motors 13 and 14 for independently
driving and controlling the crawlers 11a and 11b, respectively, reduction
mechanisms for the traveling hydraulic motors 13 and 14, etc.

[0053] The upper swing structure 20 includes a swing frame 21, an engine
22 (as a prime mover) mounted on the swing frame 21, an power
assist/generation motor 23 (charging device) driven by the engine 22, a
electric swing motor 25, a hydraulic swing motor 27, an electric double
layer capacitor 24 connected to the power assist/generation motor 23 and
the electric swing motor 25, a reduction mechanism 26 for decelerating
the rotations of the electric swing motor 25 and the hydraulic swing
motor 27, etc. Driving force of the electric swing motor 25 and the
hydraulic swing motor 27 is transmitted to the lower travel structure 10
via the reduction mechanism 26. By the driving force, the upper swing
structure 20 (swing frame 21) is driven and swung relative to the lower
travel structure 10.

[0054] The upper swing structure 20 is equipped with the shovel mechanism
(front implement) 30. The shovel mechanism 30 includes a boom 31, a boom
cylinder 32 for driving the boom 31, an arm 33 supported by a distal end
part of the boom 31 to be rotatable around an axis, an arm cylinder 34
for driving the arm 33, a bucket 35 supported by the distal end of the
arm 33 to be rotatable around an axis, a bucket cylinder 36 for driving
the bucket 35, etc.

[0055] Further, a hydraulic system 40 for driving hydraulic actuators
(such as the aforementioned traveling hydraulic motors 13 and 14,
hydraulic swing motor 27, boom cylinder 32, arm cylinder 34 and bucket
cylinder 36) is mounted on the swing frame 21 of the upper swing
structure 20. The hydraulic system 40 includes a hydraulic pump 41 (see
FIG. 2) as a hydraulic fluid source for generating the hydraulic pressure
and a control valve 42 (see FIG. 2) for driving and controlling the
actuators. The hydraulic pump 41 is driven by the engine 22.

[0056]FIG. 2 shows the system configuration of principal
electric/hydraulic devices of the hydraulic shovel. As shown in FIG. 2,
the driving force of the engine 22 is transmitted to the hydraulic pump
41. The control valve 42 controls the flow rate and the direction of the
hydraulic fluid supplied to the hydraulic swing motor 27 according to a
swing operation command (hydraulic pilot signal) from a control lever
device 72 (see FIG. 3) which is operated for the swing. The control valve
42 also controls the flow rates and the directions of the hydraulic fluid
supplied to the boom cylinder 32, the arm cylinder 34, the bucket
cylinder 36 and the traveling hydraulic motors 13 and 14 according to
operation commands (hydraulic pilot signals) from a control lever device
73 (see FIG. 3) which is operated for movements other than the swing.

[0057] An electric system is made up of the power assist/generation motor
23, the capacitor 24, the electric swing motor 25, a power control unit
55, a main contactor 56, etc. The power control unit 55 includes a
chopper 51, inverters 52 and 53, a smoothing capacitor 54, etc. The main
contactor 56 includes a main relay 57, an inrush current prevention
circuit 58, etc.

[0058] The voltage of DC power supplied from the capacitor 24 is boosted
by the chopper 51 to a prescribed bus line voltage and is inputted to the
inverter 52 (for driving the electric swing motor 25) and the inverter 53
(for driving the power assist/generation motor 23). The smoothing
capacitor 54 is used for stabilizing the bus line voltage. The electric
swing motor 25 and the hydraulic swing motor 27, whose rotating shafts
are connected to each other, cooperatively drive the upper swing
structure 20 via the reduction mechanism 26. The capacitor 24 is charged
or discharged depending on the driving status (regenerating or power
running) of the power assist/generation motor 23 and the electric swing
motor 25.

[0059] A controller 80 generates control commands for the control valve 42
and the power control unit 55 using the swing operation command signal,
pressure signals, a revolution speed signal, etc. (explained later) and
executes a variety of control, such as switching between a
hydraulic-alone swing mode and a hydraulic/electric hybrid swing mode,
swing control in each mode, abnormality monitoring of the electric system
and energy management.

[0060]FIG. 3 is a block diagram showing the system configuration and
control blocks of the hydraulic shovel. While the system configuration of
the electric/hydraulic devices shown in FIG. 3 is basically identical
with that in FIG. 2, devices, control means, control signals, etc.
necessary for carrying out the swing control in accordance with the
present invention are shown in detail in FIG. 3.

[0061] The hydraulic shovel is equipped with an ignition key 70 for
starting up the engine 22 and a gate lock lever device 71 for turning a
pilot pressure shutoff valve 76 on and thereby disabling the operation of
the hydraulic system when the operator stops the operation (work). The
hydraulic shovel is further equipped with the aforementioned controller
80 and devices (hydraulic-electric conversion units 74a, 74bR and 74bL,
electric-hydraulic conversion units 75a, 75b, 75c and 75d and a
hydraulic-alone swing mode fixation switch 77) related to the
input/output of the controller 80. These components constitute a swing
control system. The hydraulic-electric conversion units 74a, 74bR and
74bL are implemented by pressure sensors, for example. The
electric-hydraulic conversion units 75a, 75b, 75c and 75d are implemented
by solenoid proportional pressure reducing valve, for example.

[0062] The controller 80 includes an abnormality monitoring/processing
control block 81, an energy management control block 82, a
hydraulic/electric hybrid swing control block 83, a hydraulic-alone swing
control block 84, a switching control block 85, etc.

[0063] In a state in which the whole system has no abnormality and the
driving of the electric swing motor 25 is possible, the controller 80
selects the hydraulic/electric hybrid swing mode. In this case, the
switching control block 85 has selected the hydraulic/electric hybrid
swing control block 83, and thus the operation of the swing actuator is
controlled by the hydraulic/electric hybrid swing control block 83. The
hydraulic pilot signal generated according to the operator's input to the
swing control lever device 72 is converted by the hydraulic-electric
conversion unit 74a into an electric signal and inputted to the
hydraulic/electric hybrid swing control block 83. Operating pressures of
the hydraulic swing motor 27 are converted by the hydraulic-electric
conversion units 74bR and 74bL into electric signals and inputted to the
hydraulic/electric hybrid swing control block 83. A swing motor speed
signal which is outputted by an inverter (for driving the electric motor)
inside the power control unit 55 is also inputted to the
hydraulic/electric hybrid swing control block 83. The hydraulic/electric
hybrid swing control block 83 calculates command torque for the electric
swing motor 25 by performing prescribed calculations based on the
hydraulic pilot signal from the swing control lever device 72, the
operating pressure signals of the hydraulic swing motor 27 and the swing
motor speed signal, and outputs a torque command EA to the power control
unit 55. At the same time, the hydraulic/electric hybrid swing control
block 83 outputs reduced torque commands EB and EC, for reducing the
output torque of the hydraulic pump 41 and the output torque of the
hydraulic swing motor 27 by the torque outputted by the electric motor
25, to the electric-hydraulic conversion units 75a and 75b.

[0064] Meanwhile, the hydraulic pilot signal generated according to the
operator's input to the swing control lever device 72 is inputted also to
the control valve 42, by which a spool 61 (see FIG. 4) for the swing
motor is switched from its neutral position, the hydraulic fluid
discharged from the hydraulic pump 41 is supplied to the hydraulic swing
motor 27, and consequently, the hydraulic swing motor 27 is also driven
at the same time.

[0065] The amount of electricity stored in the capacitor 24 (electric
amount) increases/decreases depending on the difference between the
energy consumed by the electric motor 25 in acceleration and the energy
regenerated by the electric motor 25 in deceleration. This is controlled
by the energy management control block 82. The energy management control
block 82 performs the control so as to keep the electric amount of the
capacitor 24 within a prescribed range by outputting a power
assist/generation command ED to the power assist/generation motor 23.

[0066] When a failure, an abnormality or a warning state has occurred in
the electric system (the electric motor 25, the capacitor 24, the power
control unit 55, etc.) or the electric amount of the capacitor 24 has
gone out of the prescribed range, the abnormality monitoring/processing
control block 81 and the energy management control block 82 switch the
switching control block 85 to make it select the hydraulic-alone swing
control block 84, by which the swing mode is switched from the
hydraulic/electric hybrid swing mode to the hydraulic-alone swing mode.
Basically, the swing hydraulic system has been properly matched with the
electric swing motor 25 so as to operate in coordination with the
electric motor 25. Thus, the hydraulic-alone swing control block 84
executes the control so that the swing operability is not impaired even
without the torque of the electric motor 25, by making a correction of
increasing the drive torque of the hydraulic motor 27 and a correction of
increasing the braking torque of the hydraulic motor 27 by outputting a
swing drive property correction command EE and a swing pilot pressure
correction command EF to the electric-hydraulic conversion units 75c and
75d, respectively.

[0067] The hydraulic-alone swing mode fixation switch 77 is used when the
swing mode has to be fixed in the hydraulic-alone swing mode for some
reason (when the electric system is in failure, when a particular
attachment has to be attached, etc.). When the fixation switch 77 is
turned to its ON position, the switching control block 85 is fixed at the
position for selecting the hydraulic-alone swing control block 84.

[0068]FIG. 4 shows the details of the swing hydraulic system, wherein
elements identical with those in FIG. 3 are indicated with the same
reference characters as in FIG. 3. The control valve 42 shown in FIG. 3
has a valve component called "spool" for each actuator. In response to a
command (hydraulic pilot signal) from the control lever device 72 or 73,
a corresponding spool shifts so as to change an opening area, by which
the flow rate of the hydraulic fluid passing through each spool's channel
changes. In the swing hydraulic system shown in FIG. 4, only a part of
the circuit including the swing spool (spool for the swing) is excerpted.

[0069] The swing hydraulic system can be switched between a first mode in
which the maximum output torque of the hydraulic swing motor 27 is set at
first torque and a second mode in which the maximum output torque of the
hydraulic swing motor 27 is set at second torque higher than the first
torque. The details of the switching will be explained below.

[0070] Referring to FIG. 4, the swing hydraulic system includes the
hydraulic pump 41, the hydraulic swing motor 27, the swing spool 61,
variable over-load relief valves 62a and 62b for the swing, and a center
bypass cut valve 63 as a swing auxiliary valve.

[0071] The hydraulic pump 41 is a variable displacement pump. The
hydraulic pump 41 is equipped with a regulator 64 including a torque
control unit 64a. By the operation of the regulator 64, the tilting angle
of the hydraulic pump 41 is changed, the displacement (capacity) of the
hydraulic pump 41 is changed, and consequently, the discharge flow rate
and the output torque of the hydraulic pump 41 are changed. When the
reduced torque command EB is outputted by the hydraulic/electric hybrid
swing control block 83 (see FIG. 3) to the electric-hydraulic conversion
unit 75a, the electric-hydraulic conversion unit 75a outputs
corresponding control pressure to the torque control unit 64a of the
regulator 64. Accordingly, the torque control unit 64a changes its
setting so as to reduce the maximum output torque of the hydraulic pump
41 by the torque outputted by the electric motor 25.

[0072]FIG. 5 is a graph showing the torque control characteristics of the
hydraulic pump 41, wherein the horizontal axis represents the discharge
pressure of the hydraulic pump 41 and the vertical axis represents the
displacement of the hydraulic pump 41. The characteristics represented by
the solid lines PT and PTS indicate the maximum torque that the hydraulic
pump 41 can output.

[0073] When the hydraulic/electric hybrid swing mode has been selected and
the reduced torque command EB is being outputted to the
electric-hydraulic conversion unit 75a, the electric-hydraulic conversion
unit 75a is generating the control pressure. In this case, the setting of
the torque control unit 64a has the characteristics of the solid line PT
(first mode) where the maximum output torque has decreased from that
represented by the solid line PTS.

[0074] When the hydraulic-alone swing mode has been selected and the
reduced torque command EB is not being outputted to the
electric-hydraulic conversion unit 75a, the setting of the torque control
unit 64a changes to the characteristics of the solid line PTS (second
mode), by which the maximum output torque of the hydraulic pump 41 is
increased by the area of the hatching.

[0075] Returning to FIG. 4, the swing spool 61 has three positions A, B
and C. In response to the swing operation command (hydraulic pilot
signal) from the control lever device 72, the swing spool 61 is switched
continuously from the neutral position B to the position A or C.

[0076] The control lever device 72 includes a pressure-reducing valve
which reduces the pressure supplied from a pilot hydraulic fluid source
29 according to the operation amount of the lever. The control lever
device 72 supplies pressure corresponding to the lever operation amount
(hydraulic pilot signal) to a right pressure chamber or a left pressure
chamber of the swing spool 61.

[0077] When the swing spool 61 is at the neutral position B, the hydraulic
fluid discharged from the hydraulic pump 41 passes through a bleed-off
restrictor and the center bypass cut valve 63 and returns to the tank.

[0078] When the swing spool 61 receiving the pressure corresponding to the
lever operation amount (hydraulic pilot signal) is switched to the
position A, the hydraulic fluid from the hydraulic pump 41 is sent to the
right side of the hydraulic swing motor 27 via a meter-in restrictor at
the position A. The hydraulic fluid returning from the hydraulic swing
motor 27 returns to the tank via a meter-out restrictor at the position
A. Consequently, the hydraulic swing motor 27 rotates in a direction.

[0079] Conversely, when the swing spool 61 receiving the pressure
corresponding to the lever operation amount (hydraulic pilot signal) is
switched to the position C, the hydraulic fluid from the hydraulic pump
41 is sent to the left side of the hydraulic swing motor 27 via a
meter-in restrictor at the position C. The hydraulic fluid returning from
the hydraulic swing motor 27 returns to the tank via a meter-out
restrictor at the position C. Consequently, the hydraulic swing motor 27
rotates in a direction opposite to the case of the position A.

[0080] When the swing spool 61 is situated at an intermediate position
between the position B and the position A, the hydraulic fluid from the
hydraulic pump 41 is distributed to the bleed-off restrictor and the
meter-in restrictor. In this case, pressure corresponding to the opening
area of the bleed-off restrictor and the opening area of the center
bypass cut valve 63 develops on the inlet side of the meter-in
restrictor. By the pressure, the hydraulic fluid is supplied to the
hydraulic swing motor 27 and operating torque corresponding to the
pressure (opening area of the bleed-off restrictor) is applied to the
hydraulic swing motor 27. The hydraulic fluid discharged from the
hydraulic swing motor 27 receives resistance corresponding to the opening
area of the meter-out restrictor at that time (back pressure), by which
braking torque corresponding to the opening area of the meter-out
restrictor is generated. The same goes for cases where the swing spool 61
is situated at an intermediate position between the position B and the
position C.

[0081] When the control lever of the control lever device 72 is returned
to its neutral position and the swing spool 61 is returned to the neutral
position B, the hydraulic swing motor 27 tends to keep on rotating due to
the inertia of the upper swing structure 20 (inertial body). In this
case, when the pressure of the hydraulic fluid discharged from the
hydraulic swing motor 27 (back pressure) is about to exceed a preset
pressure of the variable over-load relief valve 62a or 62b for the swing,
the over-load relief valve 62a or 62b operates to drain part of the
hydraulic fluid into the tank, by which the increase in the back pressure
is restricted. Consequently, braking torque corresponding to the preset
pressure of the over-load relief valve 62a or 62b is generated.

[0082]FIG. 6A is a graph showing the meter-in opening area characteristic
and the bleed-off opening area characteristic of the swing spool 61 in
the first embodiment of the present invention. FIG. 6B is a graph showing
the meter-out opening area characteristic of the swing spool 61 in the
first embodiment of the present invention.

[0083] In FIG. 6A, the solid line MI indicates the meter-in opening area
characteristic in this embodiment and the solid line MB indicates the
bleed-off opening area characteristic in this embodiment. The two-dot
chain line MBO indicates a bleed-off opening area characteristic with
which satisfactory operability can be secured in a conventional hydraulic
shovel using no electric motor. The bleed-off opening area characteristic
MB in this embodiment is designed so that the opening areas at the
starting point and the end point of the control zone coincide with those
in the conventional characteristic but the opening areas in the
intermediate zone (between the starting point and the end point) are
larger than those in the conventional characteristic.

[0084] In FIG. 6B, the solid line MO indicates the meter-out opening area
characteristic in this embodiment and the two-dot chain line MOO
indicates a meter-out opening area characteristic with which satisfactory
operability can be secured in the conventional hydraulic shovel using no
electric motor. The meter-out opening area characteristic MO in this
embodiment is designed so that the opening areas at the starting point
and the end point of the control zone coincide with those in the
conventional characteristic but the opening areas in the intermediate
zone are larger than those in the conventional characteristic.

[0085]FIG. 7 is a graph showing a combined opening area characteristic of
the meter-in restrictor of the swing spool 61 and the center bypass cut
valve 63 with respect to the hydraulic pilot signal (operating pilot
pressure).

[0086] When the hydraulic/electric hybrid swing mode has been selected,
the swing drive property correction command EE is not outputted and thus
the center bypass cut valve 63 is at the open position shown in FIG. 4.
Therefore, the combined opening area characteristic of the meter-in
restrictor of the swing spool 61 and the center bypass cut valve 63 is
the characteristic indicated by the dotted line MBC (first mode) which is
determined exclusively by the bleed-off opening area characteristic MB
shown in FIG. 6A.

[0087] When the hydraulic-alone swing mode is selected, the swing drive
property correction command EE is outputted to the electric-hydraulic
conversion unit 75c as mentioned above. The electric-hydraulic conversion
unit 75c outputs corresponding control pressure to a pressure receiving
part of the center bypass cut valve 63, by which the center bypass cut
valve 63 is switched to an restrictor position (to the right of the open
position in FIG. 4). By the switching of the center bypass cut valve 63,
the combined opening area characteristic of the meter-in restrictor of
the swing spool 61 and the center bypass cut valve 63 with respect to the
hydraulic pilot signal is changed to the characteristic of the solid line
MBS (second mode) where the combined opening area is smaller than that in
the characteristic of the dotted line MBC. This combined opening area
characteristic of the solid line MBS is equivalent to the bleed-off
opening area characteristic MBO in FIG. 6A capable of securing
satisfactory operability in the conventional hydraulic shovel.

[0088] FIG. 8 is a graph showing time-series waveforms of the hydraulic
pilot signal (pilot pressure), the meter-in pressure (M/I pressure), the
assist torque of the electric swing motor 25 and the revolution speed
(swing speed) of the upper swing structure 20 in the swing driving
operation in the hydraulic/electric hybrid swing mode. From a
swing-stopped state in which the pilot pressure equals 0, the hydraulic
pilot signal (pilot pressure) was increased with time (T=T1-T4) gradually
(in a ramp-like shape) up to the maximum pilot pressure.

[0089] When the hydraulic/electric hybrid swing mode has been selected,
the combined opening area characteristic of the meter-in restrictor of
the swing spool 61 and the center bypass cut valve 63 is determined
exclusively by the bleed-off opening area characteristic MB shown in FIG.
6A as indicated by the dotted line MBC in FIG. 7. Thus, the meter-in
pressure (M/I pressure) in this embodiment becomes lower than that in the
conventional hydraulic shovel due to the larger opening area of the
bleed-off restrictor. Since the meter-in pressure corresponds to the
operating torque (acceleration torque) of the hydraulic swing motor 27,
acceleration torque compensating for the decrease in the meter-in
pressure has to be provided by the electric motor 25. In FIG. 8, the
positive assist torque means assist torque on the power running side. In
this embodiment, the control is executed so that the total sum of the
assist torque of the electric motor 25 and the acceleration torque
deriving from the meter-in pressure caused by the swing spool 61
substantially equals the acceleration torque generated in the
conventional hydraulic shovel. By this control, the swing speed of the
upper swing structure 20 is allowed to give an acceleration feeling
equivalent to that in the conventional hydraulic shovel.

[0090] In contrast, when the hydraulic-alone swing mode is selected, the
combined opening area characteristic of the meter-in restrictor of the
swing spool 61 and the center bypass cut valve 63 is changed to the
characteristic of the solid line MBS shown in FIG. 7 where the combined
opening area is smaller than that in the characteristic of the dotted
line MBC. Thus, the meter-in pressure caused by the swing spool 61
increases to the meter-in pressure acquired in the conventional hydraulic
shovel (solid line in FIG. 8) and the control is executed so that the
acceleration torque deriving from the meter-in pressure caused by the
swing spool 61 substantially equals the acceleration torque generated in
the conventional hydraulic shovel. By this control, the swing speed of
the upper swing structure 20 is allowed to give an acceleration feeling
equivalent to that in the conventional hydraulic shovel.

[0091] The fact that the upper swing structure 20 can be swung by the
hydraulic motor 27 alone means that the maximum output torque of the
hydraulic swing motor 27 is higher than that of the electric swing motor
25. This means that even if the electric motor 25 happens to operate in
an unexpected way in the hydraulic/electric hybrid swing mode, the
trouble does not lead to any substantially dangerous movement as long as
the hydraulic circuit is operating normally. Thus, the present invention
is advantageous in terms of safety as well.

[0092]FIG. 9 is a graph showing a meter-out opening area characteristic
of the swing spool 61 with respect to the hydraulic pilot signal
(operating pilot pressure).

[0093] When the hydraulic/electric hybrid swing mode has been selected,
the swing pilot pressure correction command EF is not outputted. Thus,
the meter-out opening area characteristic of the swing spool 61 is
indicated by the dotted line MOC (first mode) which exhibits variation
similar to that of the meter-out opening area characteristic MO shown in
FIG. 6B.

[0094] When the hydraulic-alone swing mode is selected, the swing pilot
pressure correction command EF is outputted to the electric-hydraulic
conversion unit 75d shown in FIG. 3 (electric-hydraulic conversion units
75dR and 75dL shown in FIG. 4) as mentioned above. The electric-hydraulic
conversion unit 75d corrects (reduces) the hydraulic pilot signal
(operating pilot pressure) generated by the control lever device 72. By
the correction of the hydraulic pilot signal, the meter-out opening area
characteristic of the swing spool 61 with respect to the hydraulic pilot
signal is changed to the characteristic of the solid line MOS in FIG. 9
(second mode) where the opening area in the intermediate zone is smaller
than that in the characteristic of the dotted line MOC. This opening area
characteristic of the solid line MOS is equivalent to the meter-out
opening area characteristic MOO in FIG. 6B capable of securing
satisfactory operability in the conventional hydraulic shovel.

[0095]FIG. 10 is a graph showing time-series waveforms of the hydraulic
pilot signal (pilot pressure), the meter-out pressure (M/O pressure), the
assist torque of the electric swing motor 25 and the revolution speed
(swing speed) of the upper swing structure 20 in a swing braking/stopping
operation in the hydraulic/electric hybrid swing mode. From the maximum
swing speed with the maximum pilot pressure, the swing speed was reduced
by decreasing the hydraulic pilot signal (pilot pressure) with time
(T=T5-T9) gradually (in a ramp-like shape) down to 0.

[0096] When the hydraulic/electric hybrid swing mode has been selected,
the meter-out opening area characteristic of the swing spool 61 with
respect to the hydraulic pilot signal exhibits variation similar to that
of the meter-out opening area characteristic MO in FIG. 6B as indicated
by the dotted line MOC in FIG. 9. Thus, the meter-out pressure (M/O
pressure) in this embodiment becomes lower than that in the conventional
hydraulic shovel due to the larger opening area of the meter-out
restrictor shown in FIG. 6B. Since the meter-out pressure corresponds to
the brake torque (braking torque), brake torque compensating for the
decrease in the meter-out pressure has to be provided by the electric
motor 25. In FIG. 10, the negative assist torque means assist torque on
the regeneration side. In this embodiment, the control is executed so
that the total sum of the assist torque of the electric motor 25 and the
brake torque deriving from the meter-out pressure caused by the swing
spool 61 substantially equals the brake torque generated in the
conventional hydraulic shovel. By this control, the swing speed of the
upper swing structure 20 is allowed to give a deceleration feeling
equivalent to that in the conventional hydraulic shovel.

[0097] In contrast, when the hydraulic-alone swing mode is selected, the
meter-out opening area characteristic of the swing spool 61 with respect
to the hydraulic pilot signal is changed to the characteristic of the
solid line MOS shown in FIG. 9 where the opening area in the intermediate
zone is smaller than that in the characteristic of the dotted line MOC.
Thus, the meter-out pressure caused by the swing spool 61 increases to
the meter-out pressure acquired in the conventional hydraulic shovel
(solid line in FIG. 10) and the control is executed so that the brake
torque deriving from the meter-out pressure caused by the swing spool 61
substantially equals the brake torque generated in the conventional
hydraulic shovel. By this control, the swing speed of the upper swing
structure 20 is allowed to give a deceleration feeling equivalent to that
in the conventional hydraulic shovel.

[0098] FIG. 11 is a graph showing relief pressure characteristics of the
variable over-load relief valves 62a and 62b for the swing.

[0099] When the hydraulic/electric hybrid swing mode has been selected and
the reduced torque command EC is being outputted to the
electric-hydraulic conversion unit 75b shown in FIG. 3
(electric-hydraulic conversion units 75bR and 75bL shown in FIG. 4), the
electric-hydraulic conversion unit 75b generates control pressure. The
control pressure acts on one side of each variable over-load relief valve
62a, 62b to reduce the preset pressure of the valve, by which the relief
characteristic of each variable over-load relief valve 62a, 62b is set at
the characteristic of the solid line SR whose relief pressure equals
Pmax1 (first mode).

[0100] When the hydraulic-alone swing mode has been selected and the
reduced torque command EC is not being outputted to the
electric-hydraulic conversion unit 75b (electric-hydraulic conversion
units 75bR and 75bL shown in FIG. 4), the electric-hydraulic conversion
unit 75b does not generate the control pressure. Thus, the relief
characteristic of each variable over-load relief valve 62a, 62b is set at
the characteristic of the solid line SRS whose relief pressure equals
Pmax2 that is higher than Pmax1 (second mode). The braking torque
increases corresponding to the increase in the relief pressure.

[0101] Thus, when the hydraulic/electric hybrid swing mode is selected,
the relief pressure of each variable over-load relief valve 62a, 62b is
set at Pmax1 that is lower than Pmax2 . When the control lever of the
control lever device 72 is returned to the neutral position, the pressure
of the hydraulic fluid discharged from the hydraulic swing motor 27 (back
pressure) rises to Pmax1 (the lower preset pressure of each variable
over-load relief valve 62a, 62b) and the control is executed so that the
total some of the assist torque of the electric motor 25 and the brake
torque deriving from the back pressure caused by the variable over-load
relief valve 62a or 62b substantially equals the brake torque generated
in the conventional hydraulic shovel. By this control, the swing speed of
the upper swing structure 20 is allowed to give a deceleration feeling
equivalent to that in the conventional hydraulic shovel.

[0102] When the hydraulic-alone swing mode is selected, the relief
pressure of each variable over-load relief valve 62a, 62b is set at Pmax2
higher than Pmax1. When the control lever of the control lever device 72
is returned to the neutral position, the pressure of the hydraulic fluid
discharged from the hydraulic swing motor 27 (back pressure) rises to
Pmax2 (the higher preset pressure of each variable over-load relief valve
62a, 62b) and the control is executed so that the brake torque deriving
from the back pressure caused by the variable over-load relief valve 62a
or 62b substantially equals the brake torque generated in the
conventional hydraulic shovel. By this control, the swing speed of the
upper swing structure 20 is allowed to give a deceleration feeling
equivalent to that in the conventional hydraulic shovel.

[0103]FIG. 12 shows a sequence for switching the swing mode from the
hydraulic/electric hybrid swing mode to the hydraulic-alone swing mode
which is executed by the abnormality monitoring/processing control block
81 of the controller 80.

[0104] The abnormality monitoring/processing control block 81 judges
whether a signal for reporting the occurrence of a failure, an
abnormality or a warning state in the electric system (the electric motor
25, the capacitor 24, the power control unit 55, etc.) (hereinafter
referred to as an "error signal") has been received from the power
control unit 55 or not (step S100). If the error signal has been
received, the abnormality monitoring/processing control block 81 further
judges whether the error signal is an error signal that requires
emergency handling (immediate action) or not (step S110). Since the mode
switching can cause a slight shock due to a valve switching operation in
the hydraulic system, etc., the abnormality monitoring/processing control
block 81 judges whether the mode switching is possible with the present
timing (at the present time) or not (step S120) unless the contents of
the error signal indicate a serious problem (emergency) needing immediate
mode switching. The abnormality monitoring/processing control block 81
carries out the mode switching (step S130) when there is no movement of
the swing structure 20 and no input to the swing control lever device 72,
or in an idling state in which there is no operation (including even a
traveling by a device other than the swing structure 20, the movement of
the front, and the input to the control lever device 73 for movements
other than the swing) at all, for example. In case of an abnormality that
can damage the system or lead to a significant failure or disaster (e.g.,
overcurrent abnormality in an inverter), the abnormality
monitoring/processing control block 81 immediately stops the electric
system and switches the swing mode to the hydraulic-alone swing mode
(S110→S130) even during operation.

[0105]FIG. 13 shows a sequence for returning the swing mode from the
hydraulic-alone swing mode to the hydraulic/electric hybrid swing mode
which is executed by the abnormality monitoring/processing control block
81 of the controller 80.

[0106] In the case where the swing mode has been switched to the
hydraulic-alone swing mode by the process shown in the flow chart of FIG.
12, the abnormality monitoring/processing control block 81 first executes
a prescribed error signal elimination process during the hydraulic-alone
swing control (step S150). In cases where the error signal was caused by
an overvoltage condition or an overtemperature condition, for example, a
process of staying on standby until elimination of the condition causing
the error signal is conducted in the error signal elimination process.
Subsequently, the abnormality monitoring/processing control block 81
judges whether the error signal has been eliminated or not (step S160).
When the error signal has been eliminated by the error signal elimination
process or in spontaneous manner, the abnormality monitoring/processing
control block 81 further judges whether the mode switching is possible
with the present timing (at the present time) or not (step S170). The
abnormality monitoring/processing control block 81 carries out the
switching to the hydraulic/electric hybrid swing mode (returning
operation) when no swing movement or operation is in progress, or in an
idling state in which there is no operation (including even the movement
of the front) at all, for example (step S180).

[0107] The hydraulic shovel in accordance with the present invention,
having the two switchable swing modes, is advantageous especially at the
startup of the machine. FIG. 14 shows a startup sequence of an ordinary
hydraulic shovel (having only a hydraulic swing motor for the swing).
When the ignition key is turned from the ON position to the START
position, the engine and the hydraulic pump are activated. Thereafter,
when the gate lock lever is released, all the hydraulic actuators
(including the swing actuator) immediately shift to their operable
states.

[0108]FIG. 15 shows a startup sequence of a conventional hybrid hydraulic
shovel using an electric motor and a hydraulic motor for the swing
driving and using a capacitor as the electricity storage device. In FIG.
15, a process executed by a controller is surrounded by dotted lines.
Such a conventional hybrid hydraulic shovel is incapable of performing
the swing operation immediately after the startup (activation) of the
engine and the hydraulic pump if the amount of electricity stored in the
capacitor (electric amount) is insufficient. Since the capacity of the
capacitor is generally small, leaving the machine (hydraulic shovel)
without starting it up for several days can lead to self-discharge of the
capacitor to an insufficient electric amount with which the swing
operation is impossible. Therefore, initial charging (step S200-step
S240) has to be executed first at the startup of the machine and the
operator has to wait on standby until the charging is finished.

[0109]FIG. 16 shows a startup sequence of the hybrid hydraulic shovel in
accordance with the present invention. In FIG. 16, a process executed by
the energy management control unit 82 of the controller 80 are surrounded
by dotted lines. In the hybrid hydraulic shovel of the present invention,
the energy management control unit 82 initially sets the swing mode in
the hydraulic-alone swing mode (initial setting) by selecting the
hydraulic-alone swing control block 84 irrespective of the electrical
condition (step S300). Therefore, when the operator shifts the gate lock
lever device 71 from a LOCK position to an UNLOCK (RELEASE) position and
thereby turns the pilot pressure shutoff valve 76 off, the hydraulic
shovel immediately shifts to its operable state. The energy management
control unit 82 executes charging/discharging control, etc. as a
background process (step S310-step S350) while the operator is operating
the hydraulic shovel and doing work. After the electric swing motor has
become drivable, the energy management control unit 82 confirms that the
mode switching is possible with the present timing (at the present time)
(step S360) and then switches the swing mode to the hydraulic/electric
hybrid swing mode (step S370).

[0110] The charging/discharging control by the energy management control
unit 82 is executed as follows: First, the energy management control unit
82 activates the power control unit 55 (step S310) and executes the
initial charging process for the inverters 52 and 53 and the smoothing
capacitor 54 and a connection process for the main contactor 56 (step
S320). Subsequently, the energy management control unit 82 judges whether
the capacitor 24 is at specified voltage or not (step S330). When the
capacitor 24 is below the specified voltage, the energy management
control unit 82 executes capacitor charging control by outputting a power
generation command to the power assist/generation motor 23. When the
capacitor 24 is above the specified voltage, the energy management
control unit 82 executes capacitor discharging control via an unshown
grid resistor by controlling the chopper 51 (step S340). When the
capacitor 24 is at the specified voltage, the energy management control
unit 82 recognizes that the preparation for the hydraulic/electric hybrid
swing mode is complete (step S350).

[0111] As described above, according to this embodiment, the hydraulic
shovel is equipped with both the hydraulic motor 27 and the electric
motor 25 for the driving of the swing structure 20 and is configured to
be switchable between the mode for executing the swing driving with the
torque of both the hydraulic motor 27 and the electric motor 25
(hydraulic/electric hybrid swing mode) and the mode for executing the
swing driving with the hydraulic motor 27 alone (hydraulic-alone swing
mode). Thus, in the hydraulic/electric hybrid swing mode, operational
actions specific to the hydraulic actuator (e.g., pressing excavation)
and operational feeling specific to the hydraulic actuator can be
realized while also achieving energy saving by regenerating the kinetic
energy of the swing structure 20 into electric energy through the
electric motor 25 at the time of braking (deceleration). Even in case of
insufficiency of the energy remaining in the capacitor 24 for storing the
regenerated electric energy, overcharging of the capacitor 24, or a
failure, abnormality or warning occurring in the electric system, it is
possible to drive the swing structure 20 with normal swing torque using
the hydraulic motor 27 alone and continue the operation of the hydraulic
shovel by the switching of the swing mode to the hydraulic-alone swing
mode. Furthermore, even when the energy remaining in the capacitor 24 is
insufficient at the startup of the hydraulic shovel, the operation (work)
can be started immediately.

[0112]FIG. 17 shows the system configuration of principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a second embodiment of the present invention. While the power
assist/generation motor 23 connected to the drive shaft of the engine 22
was used in the first embodiment shown in FIG. 2, the second embodiment
uses a hydraulic motor 101 driven by the hydraulic fluid discharged from
the hydraulic pump 41 and an electric motor 100 (charging device) having
the power generation function and connected to the drive shaft of the
hydraulic motor 101. The electricity storage device can be implemented
not only by the electric double layer capacitor 24 but also by a variety
of devices capable of storing electricity such as a lithium-ion
capacitor, a lithium-ion battery and a nickel hydride battery. In the
second embodiment shown in FIG. 17, a battery 103 such as a lithium-ion
battery is used as the electricity storage device.

[0113]FIG. 18 shows the system configuration of principal
electric/hydraulic devices of a hybrid hydraulic shovel in accordance
with a third embodiment of the present invention. In this embodiment,
voltage supplied from an electric equipment system battery line,
including an alternator 110 and an electric equipment system battery 111,
is boosted using a DC/DC converter 112 in order to conduct the initial
charging of the capacitor 24. In this case, however, the energy
management control unit 82 is required to execute the control so as to
fix the electric amount of the capacitor within a certain range only by
the acceleration/deceleration of the swing operation since surplus energy
occurring in the capacitor 24 cannot be freely released to the electric
equipment system battery line.

[0114] FIGS. 19 and 20 show the system configurations of principal
electric/hydraulic devices of hybrid hydraulic shovels in accordance with
fourth and fifth embodiments of the present invention.

[0115] While hydraulic shovels using an engine 22 as the prime mover have
been illustrated in the above embodiments, the present invention is
applicable also to hydraulic shovels using a different prime mover (e.g.,
electric motor) with no problem. The embodiment shown in FIG. 19
illustrates the system configuration of a hydraulic shovel using an
electric motor 120 which is driven by AC power from a AC power supply
121. The embodiment shown in FIG. 20 illustrates the system configuration
of a hydraulic shovel using an electric motor 120 which is driven by a
high-capacity battery 130. In the embodiment shown in FIG. 19, voltages
supplied from the AC power supply 121 are boosted using an AC/DC
converter 122 in order to conduct the initial charging of the capacitor
24 similarly to the embodiment shown in FIG. 18.

[0116] The following thing has to be taken care of when applying the
present invention to a hydraulic shovel using an electric motor 120 as
the prime mover: If the power line and the power control unit are shared
by the electric swing motor and the electric motor as the prime mover, a
failure occurring in the power line or the power control unit can disable
even the operation in the hydraulic-alone swing mode.

[0117] In the embodiment shown in FIG. 19, the main electric motor 120 is
implemented by a three-phase AC induction motor that is directly driven
by three-phase AC power from the AC power supply 121 so that the main
electric motor 120 can use a power supply line separate from that for the
electric swing motor 25 which uses the energy accumulated in the
capacitor 24. In the embodiment shown in FIG. 20, two power control units
132 and 133 are provided separately for the main control and the swing.
In case of an abnormality (e.g., short-circuit failure) occurring in the
electric swing motor 25 or the swing power control unit 133, the
operation in the hydraulic-alone swing mode is possible by detaching the
electric swing motor 25 and the swing power control unit 133 by use of a
swing electric system shutoff relay 134.

[0118] While embodiments of application of the present invention to
hydraulic shovels have been described above, the essence of the present
invention is the availability of the switching between the
hydraulic/electric hybrid swing mode and the hydraulic-alone swing mode
for the driving of the swing structure. Therefore, the present invention
is applicable also to a wide variety of other construction machines
having a swing structure.